(1) Field of the Invention
This invention relates in general to magnetic heads and in particular to so-called multitrack scanning magnetic heads.
(2) Description Relative to the Prior Art
The traditional form for a magnetic head--say a single-track record head--is a gapped mangetic core on which a coil of wire is wound. Electrical signal current in the coil induces a magnetic field within the core and, as the flux lines of the field close on themselves, they bridge, and fringe out from, the gap. A magnetic medium in contact with the head at its gap receives the gap fringing field, thereby effecting recording in the medium. Although the traditional form of magnetic head has many uses, there are, however, some instances when it is desirable to provide ancillary control of the recording function, whereby recording may be effected, or not, at will.
A traditional reproduce head similarly is comprised of a gapped magnetic core on which a "reproduce" coil is wound, the dimensions of the "reproduce" gap being, however, often different from the dimensions of the "record" gap. Signal flux patterns in a magnetic medium in contact with such a reproduce head at its gap cause flux to enter the core, link the coil thereon, and exit the core at the gap, thereby inducing signal current in the reproduce coil. Just as there are instances when it is desirable to provide ancillary control of a recording function, there are also instances when it is desirable to provide ancillary control of a reproduce function, i.e., despite the fact that the reproduce gap is in contact with a recorded flux pattern, flux is controllably precluded from coursing the core and linking the reproduce coil.
With the above as background, consider for a moment a multitrack magnetic record head comprised of a stack of head cores with their respective gaps aligned along a gap line; and imagine, for example, a common signal-carrying coil linking all such cores. By successively turning ON and OFF, each core in the stack by means of some ancillary means, each core will take a time-division sample of the signal in the common coil . . . and if the line of core gaps is in contact with a recording medium (magnetic tape), a plurality of time-division samples will be recorded in respective tracks of the medium. Such a process has been desired by those in the video recording field for some time, whereby the whole concept of linear video recording would become commercially practicable. By time-division sampling of, say, an NTSC video signal, each picture element of each line could be recorded in a respective track at a low relative head-to-tape speed, thereby obviating the need for the high relative head-to-tape speeds which are common to helical scan and quadruplex recorders. In a similar way, playback of such a multitrack recording could be effected by successively switching ON, and OFF, the cores in the stack, thereby to induce, successively, corresponding element signals in the common coil which links the cores.
The recording and playback of "video" signals are but two representative uses for the whole idea of ancillary control of the record and reproduce functions; and, obviously, many other uses may be contemplated, as well.
As will appear below, the invention utilizes to advantage the existence of a domain wall in a thin magnetic film: A domain wall in a magnetic film is a region thereof which exists between magnetizations of different orientation. Two kinds of domain walls are known to exist, i.e. Block and Neel walls, and either is applicable to the practice of the invention. With a Block wall, the magnetization vector rotates in the plane of the wall; a Neel wall, on the other hand, while existing between magnetizations of different orientation, involves a change from one magnetization orientation to another in such a way that the magnetization vector within the wall rotates in a plane formed by a vector parallel to the wall and vector perpendicular to the wall. Domain walls, as is known, may be created, destroyed, and positioned by various techniques.
In a preferred implementation of the invention, use is made of structures known as "magnetic wire memories". Such structures, which are hereinafter simply called "magnetic wires", comprise a thin film of circumferentially oriented magnetic material, e.g. permalloy, coated on an electrically conductive wire. Magnetic wires may be obtained from the Sperry Rand Corporation and General Electric Co.; and various uses for them are disclosed in U.S. Pat. Nos. 3,495,230; 4,120,011; 4,123,790; 4,136,371; 4,137,554; and 4,164,770.
With the above as background, the invention will now be summarized as follows: